4607B South Hall

One of the simplest and the most important results in elliptic theory is the maximum principle. It provides sharp estimates for the solutions to elliptic PDEs in $L^infty$ in terms of the corresponding norm of the boundary data. It holds on arbitrary domains for all (real) second order divergence form elliptic operators $- div A nabla$. The well-posedness of boundary problems in $L^p$, $p<infty$, is a far more intricate and challenging question, even in a half-space. In particular, it is known that some smoothness of $A$ in $t$, the transversal direction to the boundary, is needed.

In the present talk we shall discuss the well-posedness in $L^p$ for elliptic PDEs associated to matrices $A$ of real (possibly non-symmetric) coefficients independent on the transversal direction to the boundary. In combination with our earlier perturbation theorems, this result shows that the Dirichlet and Regularity boundary value problems are well-posed in some $L^p$, $1<p<infty$, whenever (roughly speaking) $|A(x,t)-A(x,0)|^2 dxdt/t$ is a small Carlesonmeasure.